1. Field of the Invention
The present invention relates to power, chemical, and transportation equipment engineering applications, and more particularly to methods of fuel burning in combustion chambers and to annular combustion chambers for carrying the methods into effect. The invention can find most utility when used in gas-turbine engines employing gaseous fuel such as natural gas, wherein the burning process is established on the separate fuel and air supply basis, and the fuel/primary air mixing and combustion stabilization are performed by using vortex flows.
2. Description of the Prior Art
A number of fuel-burning methods are known in the prior art, wherein in order that the flame may be stabilized, it is desirable to supply heat for ignition of the incoming air-fuel mixture to the base of the flame. In combustion chambers for gas-turbine engines, the average velocity of the fuel-air flow is invariably higher than that of turbulent combustion, so that the problems of igniting and sustaining combustion of the fuel, as well as the problems of providing a more complete fuel combustion and a specified gas flow temperature profile at the combustion chamber outlet are critical enough, since both an ineffective ignition and unstable combustion substantially reduce the operational reliability of the entire gas-turbine engine. The incomplete combustion of the fuel imposes a cost penalty on the engine, while the discrepancy between the actual temperature distribution of the gas flow proceeding at the outlet of the combustion chamber and the specified distribution results in a shorter life and poorer strength of the gas-turbine blades and hence of the entire engine.
Currently, problems pertaining to a higher furnace heat release per unit volume of the combustion chambers resulting in their shorter length and a better compactness, and attempts to reduce the content of deleterious components in the combustion products ejected to the atmosphere and to provide a reasonably low temperature level of the combustion chamber flame elements, become increasingly important.
A successful solution of these problems is largely dependent on the fuel-air mixing pattern in the burning zone of the combustion chamber and on providing stable hot gas recirculation zones therein, ensuring a reliable ignition of the fuel and sustained combustion under conditions of increased air excess in the burning zone.
A method of fuel burning is known in the art consisting in that the primary air flow, i.e., the air involved in generation and stabilization of the combustion process, is split into concentric annular streams, swirled at an angle of 45 to 60 degrees about the combustion chamber longitudinal axis, and introduced into the burning zone of the combustion chamber, the two concentric annular streams of the primary air separated by an annular stabilizer being swirled in opposite directions. Simultaneously, a fuel gas is supplied to the burning zone and mixed with the primary air to form a fuel-air mixture. In the air shadow zone, directly behind the stabilizer, a region of low pressure is produced, giving rise to a vertical recirculation flow in the burning zone, running along the combustion chamber axis, with the forward flow (downstream) of the burning fuel-air mixture and the reverse flow (upstream) of the hot combustion products. The products of combustion provide for heat supply to the incoming fuel-air stream and stabilizing the burning process. Also supplied to the mixing zone of the combustion chamber is the secondary air likewise previously divided into coaxial annular streams, which is added to the combustion products, thus reducing the temperature thereof and cooling the flame elements of the combustion chamber.
The annular combustion chamber carrying into effect this method of fuel burning, comprises two concentric annular flame tubes defining a portion of the combustion chamber burning zone and having an annular stabilizer arranged therebetween. The annular stabilizer subdivides the space between the flame tubes into two concentric annular ducts housing primary air supply members in the form of vane swirlers having angles of air swirling which are opposite in sign and providing swirling motion of the primary air annular streams in the concentric annular duct in opposite directions and admission thereof into the burning zone. The outer wall of the stabilizer, facing the burning zone, has holes provided therein for injection of the fuel into the burning zone. The secondary air supply members represent a vane swirler mounted on one of the flame tubes and displaced downstream from the primary air swirlers.
A serious disadvantage of the aforementioned method of fuel burning and of the combustion chamber carrying this method into effect resides in the reverse flow of combustion products effective in the burning zone. Such a recirculation flow pattern increases the length of the burning zone and prevents a more efficient use of the burning zone space, since a portion of its volume is taken up by the reverse flow of the combustion products, where in no combustion of the fuel-air mixture occurs.
In addition, the fuel combustion is performed with a low excess of air and, consequently, with a high temperature in the burning zone. This causes an increase in the content of deleterious constituents in combustion products ejected to the atmosphere, such as nitric exides. Furthermore, the high temperature in the burning zone gives rise to an increased heating of the fuel-delivery members of the combustion chamber, i.e., of the outer perforated wall of the stabilizer, thus resulting in a poorer serviceability of the chamber.